Vernier rheostat



Patented July 13, 1926.

WILLIAM Y. FARNSWORTH, 0F SEATTLE, WASHINGTON.

VERNIER RHEOSTAT.

Application filed J'une 28, 1922. Serial N o. 571,366.

My invention relates to improvements in rheostats, and more particularly to devices of that character known as Vernier rheostats, and which are especially desirable for use in connection with radio receiving and sending apparatus.

In the most common types of rheostats now used in radio sets, the resistance wire i'sI wound aboutv a core; one end of the wire being electrically connected with the circuit, and a blade, which is connected in the circuit, is mounted for adjustment along the coil to Contact with the dilerent windingsin order that a-varying amount otresistance may be thrown in the circuit. It is apparent, however, that in rheostats of this construction, there is a definite number of contact points and hence only a definite number of different amounts of resistance can be obtained, leaving a length of wire between each ot the contact points along which adjustment is not possible. The result of this is that, when the contactlplade is adjusted along the coil, the resistance jumps from one step to another and it is not possible to obtain an amount of resistance between amounts `thus provided for.

It is therefore the object of'this invention to provide a Vernier rheostat whereby any -desired amount of resistance that is possible within the limits of the device may be thrown into the circuit; that is:=a rheostat which has an infinite number of contact points.

A. further object of the invention resides in. the provision of a Vernier rheostat whereby the major and vernieradjustment may bermade by rotative movement of aY single adjusting knob.

Other objectsV of the invention reside in the provision of pointers whereby the relative positions of the Vernier and resistance coil blades may be indicated.

lt is also an object of this invention to embody these features of adjustment in a condenser especially useful in radio receiv ing and sending apparatus.`

Other objects of 'the invention reside in the letails ot construction of the parts embodied in the device, and inthe mode of operation.

ln. accomplishing these and other objects ot thei invention, l have provided the improved details o construction, the preferred forms of which are illustrated in the accompanying drawings, wherein- Figure l is central section oi? a Vernier ing a baseplate2 and an integral peripheralv rim, or iiange 3. Fitted within the shell is a circular platev l of an insulating material,

such as hard rubber, or libre, and extended through this and the base of the shell are screws 5, as shown in Figure 2, whereby the shell is fixed to the panel.

Fitted against the rim 3 of the shell and extending from the same, is a ring 6 of tibre which, at its inner edge, is 'fitted between the rim of the shell and edge of the plate 4l, and within this ring is fitted a circular, insulating core 7 upon which a resistance wire 8 is wound, in a series ot regularly spaced apart convolutions. One end of the resistance wire' is fixed to a binding post 9 mounted within the shell and to which a circuit wir'e 10 is connected, while the other end of the wire is lixed in the core.

Mounted coaxially of the shelhis a sleeve 11 which extends rotatably through the panel, the base of the shell and plate 4, and

at its inner end it has a collar 12 adjustable thereon that may be fixed at different points ot adjustment by means of a set screw 14 threaded through the same, and rmounted on this collar is a blade 15 which sl'idably engages the coils of resistance wire and may be adjusted to different positions along the coil to vary the resistance in the circuit.

ltotatably extended through the sleeve 11 is a shaft 16 provided at the outer lside of the panel 1 with a turning knob 17 and at its inner endr has a collar 18 adjustable thereon and secured by a set screw 19 at different points of adjustment. Mounted Vou this collar is `a Vernier blade 2O which extends beyond the resistance coil and has a downturned end wportion 21 that can be moved, by rotation of the knob 17, inV rubhing contact along a Vernier resistance wire 22 that is wound about the outer'face of the insulating` ring 6 within a groove proliet vided therein. is i'ixed in a binding post 23 mounted within the shell and to which the other circuit wire Q4 is connected` while the other end of the wire is iixed in the ring. 6, as is shown in Figure 2.- i

B'Iounted in the blade '2O is an inwardly extending post lo which extends through an arcuatelv formed slot 26 in the major resistance blade so that movement ot the latter can be efllected by the connection provided through the post and blade 2O with the shaft 16.

In this construction, the slot 26 is of such length and is so located, that a movement oit the Vernier-blade in opposite directions may be made which will cause the end thereof to move along the Iver-nier wire a distance equal to the length o't' wire in one coil .ot the resistance wire 8, without causing movement ot the major resistance blade. This provision makes possible the varying ot the amount ot resistance by manipulation ot the Vernier' between the amounts provided for by adjustment of the blade between windings of the coil.

Assuming that the parts are so constructed and assembled, and that circuit. wires 10 and Q4 are connected with the binding posts' 9 and Q3, it will be apparent that the circuit will Y[low from wire 10 along post 9, coil ot' resistance wire S, through blade 15, sha'tt 1G, blade2i), Vernier wire 22, binding post Q3 and then out on circuit wire Q4. A desired amount of 'resistance may be thrown into the circuit by turning the knob 1T to advance they blades along` the coil and vernier wires to the approximate point or just slightly beyond the desired point and then turning the Vernier blade. back to get the exact amount by cutting out part ot the vcraier wire.

The position ot the blades is indicated to the operator by means oit pointers 29 and 30 that are lixed respectively to the knob 1T and sleeve 11 at the outside of the panel 1.

It will be seen that in this way the desired amount ot' resistance may be had by adjustment o1 the major blade 15 along the coil and that any desired amount between the amounts provided by the coil may be obtained by adjustment ot the vernier blade.

It is apparent that various changes in construction of the device may be made without departing` from thel spirit ot the invention, one being in the lost motion conneotion between'the blades. It may be desired to efiect movement ot the major resistanceblade by mounting a pin in the turning shait and extending this pin through a slot provided in thesleeve on which the major resistance blade is mounted; or by the po vision of upturneo ears or projections on either member engaged with the other. y In Figures 3 and 4, I have illustrated a One end of the Vernier wire `condenser construction which operates in a manner similar to the rheostat just described. In this condenser a Vernier adjustment is also providedfor by manipulation ot the same knob whereby the major adjustment is made.

The condenser comprises a plurality ot plates 31 that aresupported in parallel, spaced relation from an insulating panel 32, by means of three screw poctsBS which have vends fixed in the panel and which extend through -the lower edges ot the plates; there being spacers 34 mounted on the screws between the plates to space them equally apart. Also mounted on the' screws are-insulated posts and 36 wherein a sleeve 37 is revolubly mounted and which extends through the panel 32 and has a. pointer 38 fixed` thereto. vCondenser plates 3) are mounted on the sleeve, to be revolved therewith to different points ot adjustmentbe-l tween the plates 31.

A shaft 40 extends revolubly through the sleeve, and this has a turning knob 41 fixed to its outer end, and a condenser plate 42 at its inner end which is adapted to be moved into and 'from between condenser plates 45 and v44 mounted in alinement` with the plates 31 at the inner ends ot the screw posts 33.

.Rotative movement of the sleeve 37 is effected by a certain connection with the knob 41: the connection comprising a stud 45 that is fixed within the pointer 38 and which extends within an arcuate slot 46 formed in a pointer plate 47 that is fixed on the inner tace ot the knob 41. The slot 46 extends through an are ot 180 degrees, which permits adjustment ot the plate 42 into and from between the platesl 43 and 44 without eilyeeting the adjustment of plates 39.

To obtain a desired adjustment of the condenser, the knob 41 is rotated until the end of slot 46 engages stud 45 and causes rotation of the sleeves 37 whereon the plates 30 are mounted to carry the blades between the plates 31. An approximate capacity may thus be obtained, then by turning back the knob to adjust the` plate 42, the exact capacity desired may be obtained.

vWhile I have illustrated a condenser having but one movable Vernier plate and two fixed Vernier plates, itis apparentthat as the capacity of the condenser is changed the number at Vernier plates may be changed correspondingly as'is necessary.

It is further noted that the arrangen'ient and location of Vernier plates with respect to the main condenser and mounting panel may be changed if desirable so that the Vernier plates are between vthe mounting panel and main plates,` and the operating connection made by means of a pin y,xed in the shatt extending on one side through a slot that may be made in the sleeve.

' Having thus described m invention, what I claim as new therein an desire to secure by Letters-Patent, is:

1 ,A'rheostat of the class described, comprising a major resistance coil having a circuit connection at one end, a Vernier' wire. having a circuit connection at one end, a major resistance blade movable in contact with the coil; said blade having a slot therein, a Vernier blade movable in contact with the Vernier wire and havin electrical connection with the major resistance blade, a turning shaft fixed to the Vernier blade and a post mounted in the Vernier blade and extended through the major `blade lslot whereby adjustment of the major blade ma y be ef- `fected by turning the shaft, and a verner adjustment may be made- Without moving the major resist-ance blade:

2. A rheostat of the class described, a circular shell, an insulating ring mountedwithin the shell, a resistance coil arranged circularly within the ring, aturningl sha-ft mounted coaxially of the shell, a sleeve revolubleon the shaft, means for electricallyl connecting one sideof an electric circuit with the coil, a Vernier wire extended about the ring, means for connecting 4 one end of the Vernier wire with the opposite side ofthe electric circuit, a blade mounted on the turning shaft and having rubbing contact with the Vernier wire, a blade mounted on 'the sleeve having rubbing contact with the resistance coil and having an arcuate slot therein and av post mounted in the Vernier blade and extended through said arcuate slot for the purpose set forth.

3. A device as in claim 2 wherein pointers are iixedv to the turning shaft and to the sleeve whereby the relative positions of the blades may be indicated.

4. ln a rheostat of the class described, a

base provided with a grooved boss and with a recess, a resistance coil housed partially within said recess and iixedly retained on the base a resistance member housed partly within t ie roove oi. said boss and also fixedly retaine on the base, a non-slidable spindle limited to rotative movement on the base,'*a plurality of contact members one of which is fixed to the Vspindle and the other is idly mounted thereon, said contact members being adapted for electrical contact with the resistance coil and the resistance mem. ber, respectively, and a lost motion connection between the two said contact members whereby the members are adapted for conjoint movement with the spindle and one member is shiftable by the spindle independently of the other member.

5. A rheostat of t-he class described, em-

bodying a base provided with an arcuate recess and with a boss concentric to said', recess, said boss having a peripheral groove, a resistance coil partly housed Within the recess, a resistance member partly housed in the groove of the boss, a non-slidable v spindle limited to rotative movement in the base, a contact arm journaled on the spindle, said arm having a recess producing a plurality of shoulders, another contact arm fixed to the spindle, and a stud fixed to the latter arm and positioned to travel within the recess and to abut the shoulders onthe other 6. A rheostat comprising an insulatingv base disk, a resistance wire secured to sai disk, a main resistance coil having an axis concentric with said wire, an axle pin through said base, a switch arm having a sov hubA lixed on said pin and having an end" 

